This invention relates to a vehicle monitoring system for monitoring a condition of a first component moving relative to a second component particularly including, but not limited to a vehicle brake actuator monitoring system for monitoring the position of the brake actuator pushrod.
There is a growing demand to monitor the condition of various vehicle components to signal the requirement for adjustment, repair or replacement. Examples are heavy vehicle brake actuators, slack adjusters, tires and the like. As described further below, the above-referenced prior application proposes a brake actuator monitoring system which includes a magnet on the moving component which, in a brake actuator is the pushrod, a sensor on the fixed component and an RF chip connected to the sensor. Reciprocal motion of the pushrod of the brake actuator may then be monitored to signal brake wear and the requirement for repair or replacement of the brake of the vehicle. However, absent a power source for the RF chip, a passive RF chip must be utilized having a very limited range or a separate source of electrical power must be provided, such as a battery. As will be recognized by those skilled in this art, it would be desirable to utilize an active RF chip to continuously monitor the condition of the moving component of the vehicle having a much greater range. A battery, however, is also subject to failure and must be periodically replaced. It would thus be desirable to utilize an active RF chip in a monitoring system of the type described and utilize the movement of the moving vehicle component as a source of electrical power for an active RF chip which is an object of this invention. The invention will now be described with regard to a brake actuator monitoring system. However, as set forth above, the vehicle monitoring system of this invention may be utilized to monitor other vehicle components provided one of the vehicle components is moving relative to the other vehicle component.
Heavy duty vehicles including trucks, buses, trailers, large recreational vehicles or coaches and the like are typically equipped with a pneumatic or air brake actuating system. The pneumatic brake actuating system applies air to a service chamber of a brake actuator to move a pushrod connected to the vehicle brake actuating system and actuate the vehicle brakes. In a diaphragm-type brake actuator, the pneumatic brake actuating system applies air pressure to one side of the diaphragm, thereby extending the pushrod to actuate the vehicle braking system. In a piston-type brake actuator, pneumatic pressure is applied to the head of the pushrod, extending the pushrod to actuate the vehicle braking system. In a piggyback brake actuator, an emergency chamber is attached to the service chamber and is operable to move the pushrod to actuate the braking system in the event that the pneumatic or air system of the vehicle fails. The emergency chamber includes a powerful spring to actuate the pushrod when there is a failure in the pneumatic system of the vehicle. The power spring also actuates the pushrod when the vehicle is parked thereby serving as a parking brake.
A brake actuator has a predetermined available movement or stroke for the pushrod. The movement of the pushrod required to fully actuate the braking system of the vehicle must be carefully monitored, such that it is within the stroke of the brake actuator. Typically, excessive movement is due to brake lining wear. As the brakes wear, greater movement of the pushrod is required to actuate the brakes. Further, as the linkages, connections, etc. between the components connecting the pushrod to the brakes may bend or become loose or excessively worn, requiring additional pushrod movement to adequately stroke the brake. A combination of these several factors may cause the available pushrod movement required to actuate the braking system of the vehicle to approach the available pushrod stroke from the brake actuator. As will be understood from those skilled in this art, this condition requires prompt maintenance of the braking system of the vehicle to avoid an unsafe condition.
The prior art has attempted to monitor pushrod movement during actuation of the braking system of the vehicle and provide an indication to an operator when there is excessive pushrod movement. The determination of when there is excessive pushrod movement is dependent upon the design or rated stroke of the brake actuator. In addition, an apparatus known as a xe2x80x9cslack adjusterxe2x80x9d is typically placed between the pushrod and the vehicle foundation brake. The slack adjuster is incrementally adjusted to compensate for slack in the braking system and to decrease the required pushrod movement of the brake actuator. Automatic slack adjusters are now available which automatically adjust the foundation brake system of the vehicle.
Electronic stroke indicator systems for brake actuators have also been proposed, particularly including the prior patents of the assignee of this application. However, there are several obstacles to overcome. First, powering and monitoring electronic stroke indicators for brake actuators on each brake actuator of an 18-wheel heavy vehicle is costly. The cost of wiring alone for the vehicle generally exceeds the cost of all the electronic indicators and monitoring equipment combined. Further, the hostile environment in which the brake actuators are monitored on the undercarriage of the heavy vehicle can damage wires connecting the brake actuator to a controller for example. Further, there are numerous configurations for the trailer as well as the cab in a tractor-trailer combination. Each axle must include a spring brake actuator as well as a service brake actuator. For efficiency and to reduce costs, it would be most desirable to utilize an xe2x80x9cactivexe2x80x9d RF chip to eliminate the requirement for wires between the electronic brake actuator indicator systems. However, as set forth above, an active RF chip requires power or electronic current to activate the active RF chip. The vehicle monitoring system of this invention provides power to an active RF chip without requiring a battery, thus eliminating the requirement for wires between the vehicle monitoring system and a receiver as set forth below.
As set forth above, the vehicle monitoring system of this invention may be utilized for monitoring a condition of a first vehicle component moving relative to a second component and is therefore not limited to monitoring the stroke of a pushrod of a brake actuator. However, the vehicle monitoring system of this invention is particularly, but not exclusively, suitable for electronically monitoring the stroke of a brake actuator pushrod, wherein the brake actuator housing is fixed relative to the vehicle and the pushrod periodically moves relative to the housing upon actuation of the vehicle braking system.
In the vehicle monitoring system of this invention, one of the first and second components includes a magnet and the other component includes an electrically conductive coil within the magnetic field of the magnet. A sensor is connected to the coil and an active RF chip is connected to the coil and the sensor which monitors the movement of the magnet relative to the electronically conductive coil. The relative movement of the magnet and the coil generates an electric current which activates the RF chip to signal a receiver of the condition of the second or moving component. In a preferred embodiment of the vehicle monitoring system of this invention, the magnet is located within the coil or more preferably moves or reciprocates through the coil thereby providing sufficient electrical current to the active RF chip to signal a remote receiver of the condition of the first component of the vehicle monitoring system.
As set forth above, in a preferred embodiment of the vehicle monitoring system of this invention, the first or fixed component is a brake actuator including a housing having an opening through the housing and the second component is a pushrod reciprocating through the opening in the housing and actuating the vehicle braking system. In a preferred embodiment, the magnet is fixed on the pushrod and the electrically conductive coil is fixed relative to the housing, surrounding the opening through the housing. In the disclosed embodiment, the magnet comprises an elongated strip including a series of magnets in end to end relation and the sensor thus continuously senses the precise position of the pushrod as it reciprocates through the housing opening to actuate the vehicle foundation brake. The electrically conductive coil may be incorporated or potted in a sleeve which surrounds the opening through the housing, such as a conventional polymeric stone shield. The sensor is preferably located adjacent the opening through the housing and may also be incorporated or potted in the stone shield. Finally, the active RF chip may also be incorporated or potted in the stone shield, providing a fixed secure assembly which is not vulnerable to the adverse environment of a brake actuator.
The vehicle brake actuator monitoring system of this invention may be utilized to sense and signal various conditions of the brake actuator, including an overstroke condition, wherein the stroke of the pushrod is nearing or has reached an overstroke condition, signaling the vehicle operator or maintenance worker that maintenance of the vehicle foundation brake is required. However, the brake actuator monitoring systems of this invention may be utilized to signal other conditions of the brake actuator including a xe2x80x9changing brakexe2x80x9d condition, wherein the brake actuator fails to extend during braking, such as when the pneumatic braking system of the vehicle is removed from park. The brake actuator monitoring system of this invention may also be utilized to signal other conditions including, for example, a defective spring.
Other advantages and meritorious features of the vehicle monitoring system and brake monitoring system of this invention will be more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.